Field of the Invention
The invention relates to a meter for recording the electricity consumption of electrical energy drawn off by a consumer from a supply network and/or for determining the electrical energy provided by a power producer to a supply network.
Description of the Background Art
A voltage dependent meter, which is often also called an electricity or watthour meter, is typically provided in each household to measure the electrical power drawn off from a supply network or the drawn-off electrical work for the purpose of consumption-based billing. To this end, typically the active current (alternating or three-phase current) and the currently applied active voltage, called the supply voltage hereafter, are measured. The utilized active energy in kilowatt hours (kWh) is determined by multiplying the current (active current) and voltage (active voltage) to obtain the electric power (P=U·I) and subsequent time integration of the electric power.
In the case of industrial consumers with especially high power peaks, power meters can also be provided, which in addition to the drawn-off electrical energy record whether the energy was drawn from the network within a relatively short time requiring an especially high power. These power peaks stress the supply network in particular and are to be billed accordingly. Similar meters are also located at entry points, such as, e.g., in solar photovoltaic roof systems or in wind turbines, to determine the electrical energy supplied by such an energy producer to a supply network.
Meters of the aforementioned type are known, e.g., from EP 0 801 836 B1 and from US 2009/0150100 A1 and U.S. Pat. No. 5,059,896. In the publication mentioned last, a watthour measuring device is described, which can be configured digitally, in order to operate as a type of different measuring device types.
In connection with the energy withdrawal from the supply network and the energy feed-in into the supply network, achieving a sufficient stability of the supply network is also desirable. The example of night storage heating can be used to clearly outline the problems associated therewith. Thus, the typical night storage heating is set up and intended to take up the electrical energy provided by the base load power plant during the off-peak periods generally occurring primarily at night and to supply it later during the day when the thermal energy is needed.
Because of the increasing distribution of alternative energies from wind and solar power plants, these cannot be used reasonably at present with a high generated energy demand and are therefore partially in remote storage, to buy them again at a later time; this is associated with corresponding costs. The shutting down of the power plant based on the conversion of renewable energy can be considered, as a result of which, however, producible energy cannot be generated per se. Alternatively for the interim storage of currently available, but not presently needed energy, an energy storage device is needed, such as, for example, a pumped storage power plant for large amounts of energy or night storage heating or underfloor heating for relatively small amounts of energy. A similar observation can be made about refrigeration devices, such as, e.g., a cold storage warehouse, which can be reduced beyond the required minus temperature, to store electrical energy in the form of cold, which otherwise must be drawn from the supply network at a time possibly unfavorable in terms of the supply network.
Without a functioning storage of electrical energy, instabilities in the network occur which are caused to a great extent by the use of renewable energy sources. It should be noted in this case that each feed-in of electrical energy tends to increase voltage, whereas each energy withdrawal tends to decrease voltage. Because the voltage-raising feed-in can be subject to rapid changes, the voltage level can also change at the assigned network connection point. In a photovoltaic system, local cloudiness may cause, for example, a 90% power drop, so that particularly in the case of larger wind power plants (wind farms) and in solar power plants the voltage in the supply network can vary on-site accordingly depending on the local weather conditions.
A so-called smart meter is known for turning on electricity-using devices, for example, household devices such as washing machines, driers, or the like at a time suitable from the viewpoint of the energy producer. In conjunction with such a smart meter, known, e.g., from the DE 10 2010 027 170 A1, such household appliances continue to operate according to their programming, however, after they are turned on, regardless of how the network situation has evolved during the on-time.
Particularly with alternative energy production, however, the production situation can change within a short time interval, for example, even within a minute, which is not taken into account by the smart meter. Disadvantageously, such smart meters are also very costly. In addition, the control of the smart meter by means of a control signal imposed on the supply voltage or separately transmitted requires large expenditures in terms of control and communication technology. The communication channels in particular result in considerable costs in the long term.
Further, a smart meter must be controlled to receive or deliver power. The current voltage situation on site continues to be disregarded, however. Thus, it cannot be ruled out that the local or supply network is to take up more energy, but the smart meters are controlled for power uptake, although at a site in the local network the maximum load, e.g., due to an industrial plant, has already been reached, and with a further power consumption by private households the network would fall below the limit in regard to its voltage. In addition, at another site due to the feed-in of power (solar current) generated by a photovoltaic plant it could be necessary to take up much more energy. The smart meter, however, regulates all consumers in the network as a whole.